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  4. The arrangement of the nuclei in a normal embryo sac in the dicot plants is-

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Q. The arrangement of the nuclei in a normal embryo sac in the dicot plants is-

AIPMTAIPMT 2006Sexual Reproduction in Flowering Plants

Solution:

Megaspore is the initial cell or beginning of female gametophyte or embryo sac. The nucleus of megaspore undergoes divisions and gives rise to embryo sac or female gametophyte, which is called megagametogenesis. During development, the single nucleus of functional megaspore (of chalazal end) undergoes 3 mitotic divisions to form 8 nuclei. Out of these 8 nuclei, 4 are present at micropylar end and 4 at chalazal end. One nucleus from each group comes in centre to form 2 polar nuclei. Remaining 3 nuclei at micropylar end constitute egg apparatus and remaining 3 nuclei at chalazal end constitute 3 antipodal cells or antipodals. So it is 3 + 2 + 3 arrangement. So fully developed normal type of female gametophyte or embryo sac is 8-nucleated and 7-celled structure.